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The Obama administration is declaring a Syrian rebel group with alleged ties to al-Qaeda as a terrorist organization. It's an effort to blunt the influence of extremists as the U.S. steps up co-operation with the Syrian opposition.

The U.S. State Department's action blocks Jabhat al-Nusra's assets in the U.S. and bars Americans from doing business with the group.

The move hasn't been announced officially but was included in the Federal Register on Monday. The department said the group was part of al-Qaeda in Iraq.

Jabhat al-Nusra has claimed responsibility for suicide bombings on Syrian government targets, raising fears of growing Islamic extremism among the opposition.

Secretary of State Hillary Clinton is travelling to North Africa this week to try to bolster moderates hoping to end Syrian President Bashar al-Assad's regime.